Such propulsion thruster uses as a fuel primarily hydrazine (N.sub.2 H.sub.4). The hydrazine is decomposed, thereby producing a substantial amount of heat, whereby the decomposition, of the propulsion gas produces the required thrust when exhausting out of a nozzle for orbit and attitude control. However, it has been a problem to increase the possible thrust produced by the propulsion gas by further heating such propulsion gas.
German Patent Publication (DE-OS) 3,128,735 discloses a propulsion thruster of the type mentioned above. The known propulsion thruster comprises a heating device arranged upstream of the nozzle as viewed in the gas flow direction. The heating device comprises a metallic pipe which is heated by the direct passage of an electrical current through the pipe. Such a pipe is constructed in the form of a long spiral or helix, whereby the propulsion gas first flows in contact with the outer surface of the heating-up device and then close to the nozzle enters into the heating pipe. The propulsion gases thus heated to a higher heat content finally enter into a central leading tube to the propulsion nozzle.
The just mentioned conventional gas heating pipe has the disadvantage that the pipe itself which functions as a heat exchanger is the electrical conductor. Moreover, the arrangement is limited to a single heating pipe since it is not feasible to split the gas stream for flowing through several heating pipes. Thus, when the heating pipe fails, a substantial reduction in the power output is unavoidable.
Another disadvantage of the prior art heating pipe is seen in that the pipe due to its helical shape, and due to the maximally occurring temperatures of up to 2300.degree. C. can be made only of rhenium. Further, the conventional heating pipe is not easily modified for adaptation to special situations or requirements. Particularly, the known system is not capable of a further substantial thrust increase by way of further heating the propulsion gases while simultaneously keeping the structure as compact as possible.